Offshore Structure Assembly Using Underwater Conical Ring Connections
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Solution Overview
Problem
The installation of fixed offshore structures, particularly in low to medium water depths, faces challenges with unreliable and time-consuming grouted connections, which are prone to corrosion and require complex maintenance, and the increasing size and weight of wind turbines exceed the lifting capacity of existing crane vessels, necessitating more expensive and cumbersome underwater connections.
Innovation Solution
The method employs an in-line connection using multiple sets of conical rings that are corrosion-resistant and low-maintenance, allowing for easy installation without grouting or bolting, enabling the connection of seabed fixation and superstructure components underwater, facilitating modular assembly and reducing the need for large, expensive crane vessels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If grouted connections are used for underwater installation, then the connection can be established below sea level, but the connection becomes time-consuming and unreliable
Solution Approach 1:
The connection system is segmented into modular components: a lower part with an outer conical ring and an upper part with an inner conical ring. This segmentation allows for standardized, pre-fabricated modules that can be quickly assembled underwater without grouting, improving both ease of operation and reliability through precise factory manufacturing of the conical interfaces.
Solution Approach 2:
The conical rings act as intermediary elements between the lower and upper parts. The inner conical ring fits within the outer conical ring to form a friction-based mechanical connection, serving as a mediator that transfers loads while eliminating the need for grout or complex bolting operations underwater.
2Reliability
If bolted flange connections are used, then the connection can be made above water, but fabrication costs increase and regular inspections are required
Solution Approach 1:
The bolted flange connection system is extracted and replaced with a pure friction-based conical ring interface. The complex bolting mechanism is taken out, leaving only the essential friction contact between conical surfaces, which eliminates corrosion issues, reduces fabrication costs, and removes the need for regular pretension inspections.
Solution Approach 2:
The conical ring connection is designed as a simple, inexpensive alternative to expensive bolted flanges. The friction interface requires no high-strength bolts, welding, or complex fabrication, making it a cost-effective solution that can be manufactured more cheaply while providing sufficient reliability for the application.
3Productivity
If wind turbine size increases to reduce costs, then energy generation efficiency improves, but lifting capacity requirements exceed available crane vessel capabilities
Solution Approach 1:
The wind turbine structure is segmented into modular parts (seabed fixation part, substructure part, transition piece, superstructure) that can be manufactured separately and assembled in a standardized sequence. This segmentation allows each component to be optimized for manufacturing and transportation while the standardized conical ring connections enable efficient assembly without requiring excessively large crane vessels.
Solution Approach 2:
The connection method changes the physical parameters of the joining process by using friction-based conical ring interfaces instead of heavy bolting or grouting. This parameter change reduces the lifting capacity requirements during installation, allowing larger wind turbines to be assembled with available crane vessel capabilities while maintaining structural integrity.
4Productivity
If more connections are made to accommodate larger turbines, then installation complexity increases, but the conical ring system reduces connection time and cost
Solution Approach 1:
The conical ring connection design is universal and can be applied to all connection points in the offshore structure (seabed fixation to substructure, substructure to transition piece, transition piece to superstructure). This multi-functional standardized connection reduces overall system complexity by using the same simple friction-based interface throughout, eliminating the need for different connection types and reducing installation time.
Data Source
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AI summary
Method for installing an offshore structure at an offshore site having a sea bottom and a water depth defining a sea level; the offshore structure including a seabed fixation structure, a transition piece and a superstructure; the method comprising installing the seabed fixation structure to the sea bottom, such that the seabed fixation structure at least partly extends above the sea bottom; positioning the transition piece on the seabed fixation structure, wherein at least an upper side of the transition piece is above the sea level; positioning the superstructure on the transition piece such that the superstructure is extending above the sea level; wherein the connection between the transition piece and the seabed fixation structure and the connection between the transition piece and the superstructure is provided as an in-line connection comprising multiple sets of conical rings engaging each other; wherein at least one of the in-line connections is at least partly below the sea level.